tailieunhanh - Cracker Handbook 1.0 part 48

Tham khảo tài liệu 'cracker handbook part 48', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Syntax CLI This instruction turns off the interruptions flag disabling this way those maskarable interruptions. A maskarable interruptions is that one whose functions are deactivated when IF 0. CMC INSTRUCTION Purpose To complement the cartage flag. Syntax CMC This instruction complements the state of the CF flag if CF 0 the instructions equals it to 1 and if the instruction is 1 it equals it to 0. We could say that it only inverts the value of the flag. STC INSTRUCTION Purpose To activate the cartage flag. Syntax STC This instruction puts the CF flag in 1. STD INSTRUCTION Purpose To activate the address flag. Syntax STD The STD instruction puts the DF flag in 1. STI INSTRUCTION Purpose To activate the interruption flag. Syntax STI The instruction activates the IF flag and this enables the maskarable external interruptions the ones which only function when IF 1 . 5 Interruptions and file managing Table of Contents Internal hardware interruptions External hardware interruptions Software interruptions Most Common interruptions Internal hardware interruptions Internal interruptions are generated by certain events which come during the execution of a program. This type of interruptions are managed on their totality by the hardware and it is not possible to modify them. A clear example of this type of interruptions is the one which actualizes the counter of the computer internal clock the hardware makes the call to this interruption several times during a second in order to maintain the time to date. Even though we cannot directly manage this interruption since we cannot control the time dating by means of software it is possible to use its effects on the computer to our benefit for example to create a virtual clock dated continuously thanks to the clock s internal counter. We only have to write a program which reads the actual value of the counter and to translates it into an understandable format for the user. External hardware interruptions .